[olug] Slow read speeds-SuSE

Charles Bird cbird.omaha at gmail.com
Wed Apr 28 23:40:19 UTC 2010

In some instances, I've seen high CPU load compressing the image while
sending over the network, and NIC doesnt have offload, thus creating an
issue where the machine has issues sending at a reasonable rate across the
network. Issue can be compounded even more with software raid.

On Wed, Apr 28, 2010 at 5:27 PM, Christopher Cashell <topher-olug at zyp.org>wrote:

> On Wed, Apr 28, 2010 at 4:16 PM, Craig Wolf <CJWolf at mpsomaha.org> wrote:
> > Ok, my backups from one of my linux servers takes 5 days to finish...my
> window is 36 hours, not working right.  Throughput of about 1.5GB/hour.
> > So in my testing, copying a 158MB directory to the server takes about 1
> Minute 5 seconds.  Copying same structure off the box takes almost 7
> minutes.  Network switches show no issues/error.  iostat shows slow to no
> throughput at all on read.
> >
> > SO, the million dollar question is, what should I look at for fixing
> this??  Do I use hdparm?
> First thing, divide and conquer.  You need to isolate the problem.
> Based on what you've said, the two likely culprits are slow disk or
> slow network.
> Try copying files from one partition to another partition (preferably
> involving the partition where the backups are being read/written
> to/from).  Check your copy speed.  Is it fast?  Is it slow?  If it's
> fast, then it's not a disk issue.  If it's slow, we need to further
> investigate the disk.
> If it is fast, then it's probably a network issue.  Check the network
> settings.  What kind of switch is this?  GigE?  Is the switch port and
> server port configured the same?  What does ethtool or mii-tool tell
> you about the interfaces?  If one side (server or switch) is set to
> autonegotiate and the other side isn't, you'll often end up at 10BaseT
> and half duplex.  If your network settings are all clean and good,
> then test the network performance.  Use iperf or even just dd
> /dev/zero into netcat to a remote box that listens with netcat and
> redirects to /dev/null.
> Hopefully that will give you a better idea of where to push forward
> with further investigation.
> > Craig Wolf
> --
> Christopher
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